An ink jet printer or the like is provided with an ink jet head in which ink droplets are ejected through nozzles.
For example, the ink jet head has a nozzle plate in which a plurality of nozzle openings are formed and a cavity plate for forming cavities each corresponding to each of the plurality of nozzle openings in which ink is filled in cooperation with the nozzle plate so that the nozzle plate and the cavity plate are joined to each other (see Japanese Laid-open Patent Applications Nos. Hei. 11-28820 and Hei. 9-57915, for example). In such an ink jet head, each of the nozzle openings is communicated with the corresponding cavity, and ink droplets are to be ejected through each of the nozzle openings.
The cavity plate is normally constituted from silicon. As an ink jet printer has a high image quality, high density of nozzles is improved. Thus, it is necessary to reduce the difference between coefficients of linear expansion of the nozzle plate and the cavity plate. For this reason, both a nozzle plate and a cavity plate are constituted from silicon in the prior art mentioned above. Further, as high density of nozzles is improved, it is necessary to make a nozzle plate thinner and reduce channel resistance of the nozzle.
In Japanese Laid-open Patent Application No. Hei. 11-28820, when manufacturing such a nozzle plate, a nozzle length is adjusted by forming a nozzle opening from one major surface of a silicon substrate by means of an anisotropy dry etching process using ICP discharge and then digging a portion of the silicon substrate from the other major surface thereof by means of an anisotropy wet etching process.
On the other hand, in Japanese Laid-open Patent Application No. Hei. 9-57915, nozzle openings are formed by polishing a silicon substrate to a predetermined thickness in advance and then subjecting both major surfaces of the silicon substrate to a dry etching process.
However, when high density of nozzles is further improved, it is necessary to make the thickness of the silicon substrate thinner further. The prior arts described above do not disclose how the silicon substrate is processed in this case. If processing of the silicon substrate is carried out while the silicon substrate is put on a stage or the like in a processing apparatus as it is, the silicon substrate is easily broken or cracked during the manufacturing process. Thus, a yield of manufacturing nozzle plates is lowered. As a result, there is fear that this brings about high costs of the nozzle plate.